As a hollow-type strain wave gearing provided with a unit hollow portion passing therethrough in the axial direction, there is known one that is provided with a cup-shaped flexible externally-toothed gear. Patent Document 1 discloses an actuator configured so that a hollow-type strain wave reduction gearing and a hollow motor are integrally connected in the axial direction.
A wave generator of the hollow-type strain wave reduction gearing has an elliptically-contoured cam plate (plug) integrally formed on the outer peripheral surface portion of a hollow rotation shaft positioned inside the flexible externally-toothed gear, and a wave bearing (wave generator bearing) mounted on the elliptical outer peripheral surface of the cam plate. The rotation shaft is formed integrally with an annular retainer holding plate on a position adjacent to the cam plate forming portion of the rotation shaft. The retainer of the wave bearing is prevented from coining off in the rotation center axis line by the retainer holding plate. Further, the shaft end portion of the rotation shaft positioned on the boss side of the flexible externally-toothed gear is supported from outer peripheral side by a bearing mounted on the bearing holder attached to the boss.